U.S. Pat. No. 4,765,370 shows a fluid control element comprising a housing in which two control chambers are formed, which are each isolated from each other and comprise a working port each as well as two pressure ports, two of the ports being provided with a sealing seat each. The fluid control element further comprises a switching element movably mounted in the housing and comprising a sealing part in each control chamber, the sealing part cooperating with the sealing seats such that these are opened or closed, and still further comprises an actuating member for the switching element. This fluid control element represents a 4/2-way valve for actuating hydraulic actuator cylinders, for example. When actuating, for example, a double-acting hydraulic cylinder, the working port of the one control chamber is connected to a working port of the hydraulic cylinder and the working port of the other control chamber is connected to the other working chamber of the hydraulic cylinder. In a first position of the switching element, the resting position, the one working chamber of the hydraulic cylinder is pressurized so that a movement occurs in a first direction, whilst in an activated position of the switching element into which the switching element is moved by an electric magnet, the other working chamber of the hydraulic piston is pressurized so that a movement occurs in the opposite direction.
It is often required, however, in addition to a movement of the hydraulic piston in a first and a second direction that the hydraulic piston, for example, is maintained fixed in a position or is freely movable. For this purpose 4/3-way valves are needed as described with reference to FIG. 13. Illustrated schematically in FIG. 13 is a hydraulic piston 1 disposed between two working chambers 2, 3. The working chamber 2 is connected to a working port A of a 4/3-way control element illustrated schematically and identified by reference numeral 10, and the working chamber 3 is connected to a working port B. Furthermore, two pressure ports P, R are provided, port P providing a pressurized fluid and port R forming a return flow conduit.
The control element shown as example 1 permits three operating conditions. In the left-hand switching position the hydraulic piston 1 is biased so as to move to the right. In the middle switching position the hydraulic piston 1 is blocked. In the left-hand switching position the hydraulic piston 1 is biased so as to move to the left.
The examples 2 and 3 likewise make possible three switching positions, the left-hand and the right-hand switching positions in each case corresponding to the right-hand and left-hand switching positions of the first example. The middle switching position in example 2 results in the hydraulic piston 1 being freely movable and the middle switching position of example 3 results in the hydraulic piston 1 being blocked by the pressure furnished by the pressure port P.
Hitherto, achieving such switching functions necessitated the use of piloted slide valves.
The object of the invention consists in providing a simple, direct-acting control element having a 4/3 operational mode to thus reduce the expense in terms of technical equipment in actuating a cylinder and to permit a more direct and faster operation of actuator cylinders and actuators, respectively.